Propellants and method of producing the same

ABSTRACT

1. A new article of manufacture, a propellant comprising about 21.0 percent nitrocellulose, about 13.0 percent nitroglycerine, about 55.4 percent potassium perchlorate of an average particle diameter of 7.5 + OR - 0.5 mu, about 9.0 percent carbon black, about 1.0 percent centralite No. 1, 0.3 percent magnesium oxide and 0.3 percent magnesium stearate, the nitrocellulose and nitroglycerine being colloided and intimately mixed with the other ingredients to form a matrix in which the particles of potassium perchlorate and carbon black are distributed.

United States- Patent 11 1 Kincaid et al.

1111 3,856,590 451 Dec. 24, 1974 PROPELLANTS AND METHOD OF PRODUCING THE SAME [75] Inventors: John F. Kincaid, Jefferson 7 Township; Louis P. Hammett, Pittsburgh, both of Pa.; Benjamin P. Dailey, Cumberland, Md.

[73] Assignee: The United States of America as represented by the Director, Office of Scientific Research and Development, Washington, DC.

22 Filed: Apr. 18,1945

21 Appl. No; 589,090

[52] US. Cl 149/l9.8, 149/21, 149/79, 149/97, 149/113 [51] Int. Cl. C06d 5/06 [58] Field of Search 52/22, 21, 21.1, 21.2, 52/20 .1, 20.2, 20,13.3,18 P, .5; 149/19.8, 2,

[56] References Cited UNITED STATES PATENTS 976,211 11/1910 DuPont 52/21 1,627,638 5/1927 DuPont 52/201 2,007,223 7/1935 Spaeth 52/22 x 2,120,324 6/1938 Dickerman 52/133 X 2,159,208 5/1939 Goodyear 52 201 x 2,385,135 9/1945 Holmes 52 7 2,408,252 9/1946 Ganahl 52/.5

FOREIGN PATENTS OR APPLICATIONS 4,179 1875 Great Britain 52/22 Primary Examiner-Benjamin R. Padgett Attorney, Agent, or FirmEugene E. Stevens, Ill

EXEMPLARY CLAIM which the particles of potassium perchlorate and carbon black are distributed.

1 Claim, No Drawings PROPELLANTS AND METHOD OF PRODUCING THE SAME The present invention relates generally to gas generating compositions and more particularly to a new and improved propellant suitable for the production of a high velocity gas jet, the reactive effect of which may be employed for the propulsion of rocket projectiles, for assisting the take-off of aircraft or for other jet propulsion purposes. v

As more fully described in the copending application of Hammet and Thomas, Ser. No. 550,905, filed Aug. 23, 1944, a propellant that is employed for jet propulsion purposes should be characterized by a combination of properties which may beregarded as the fundamental prerequisites for satisfactory performance. These fundamental properties include the following:

1. A high Specific impulse, i.e., a high total impulse (force-time integral) imparted to the rocket per unitweight of propellant consumed;

2. Reproducible internal ballistics, i.e., a burning rate' that deviated only slightly, if at all, from the so-called burning law which may be conveniently expressed in V the form P (Ag/A )lI(lNl where P is the steady state pressure in the rocket motor; Ag is the total burning area of the grain or fuel; At is the area of the orifice or throat of the motor and n is a number less than unity.

' 3. A low value of the exponential constant n in the burning law,- corresponding to a low dependence of burning rate of the'pressure existing in the rocket motOl.

4. A low temperature coefficient of pressure change when a fuel of given grain size is fired at various preignition temperatures in a given motor, the temperature coefficient being conveniently defined by the relation:

where-P is the pressure in the rocket motor, T is the pre-ignition temperature, R is the rate of burning, K is a constant Ag/At ratio, and n is the exponential constant in the burning law. There are many other proper ties that are desirable in a rocket fuel, for example high loading density, high mechanical strength, moderate motor chamber requirements, etc., but the four basic properties listed above are of controlling importance if reliable performance under a wide range of climatic conditions is to be obtained.

As indicated above, prior to the development of Composite Propellants, no rocket fuel was available that met the above fundamental prerequisites. Thus ballistite, perhaps the most widely used rocket propellant at the present time, while satisfactory in respect to specific impulse and conformance to the burning law, has a large exponential constant n (about 0.73), corresponding to a high dependence of burning rate on pressure; and a high temperature coefficient (about 1.5 percent), corresponding to a percent change in motor pressure for every 10C. change in pre-ignition temperature. As a result, reproducible results over a wide range of climatic conditions are practically impossible to obtain when ballistite is used as the rocket fuel.

In this and other respects the composite propellants described and claimed in Hammett and Thomas application Ser. No. 550,905 represent a significant improvement in fuels designed for jet propulsion uses. These composite'propellants consist of a compacted mass of finely divided particulate gas generating materials bonded together by thermosetting synthetic resin which, because of its essentially inert character, is used in an amount merely sufficient to impart the desired degree of mechanical strength and rigidity to the composition. Such propellants are prepared by incorporating a small proportion of uncured thermosetting resin with the particulate material, compressing the resulting powdery composition under considerable pressure into grains of suitable shape and then curing the grains after removal from the mold. The finished grains are characterized by a high specific impulse, very low deviation from the gas law, a low exponential constant (less than 0.5) and a low temperature coefficient (ca. 0.3 percent/C.).

it will be apparent that the Hammett-Thomas Composite Propellants constituted the first rocket propellant fuels that met the four basic prerequisites for satisfactory performance. However, the production difficulties created by this radical departure in the art were considerable. Thus the powdery composition from which grains were prepared required the use of high pressure compression molding presses a type of equipment not readily available in existing explosives facilities. Furthermore, the production methods necessitated by the character of the fuel were not adaptable to the production of thin webbed grains. Again, the large proportion of particulate filler and the very small proportion of binder employed resulted in a relatively brittle grain which required the use of resilient mounting in rocket motors. Finally, the methods of fabrication'dictated by the character of the fuel were not amenable to the production of very long grains except by cementing a plurality of grains together. For these and other reasons, the Composite Propellants were restricted to applications requiring relatively large size grains.

The object of the present invention is to provide a new and improved jet propulsion fuel that is characterized by a low temperature coefficient of burning and which is readily adaptable to large scale production using conventional propellant manufacturing equipment. I

A more particular object is to provide a jet propulsion fuel having-a temperature coefficient comparable to that of a compression-molded type of Composite Propellant but which can be economically manufactured in thin web granulations using conventional solvent-extrusion equipment such as that employed in the manufacture of double base powders.

Another object is the provision of an improved type of Composite Propellant that can be readily manufactured in either thin web granulations or in large grain sizes.

Still another object is an improved jet propulsion fuel characterized not only by a low dependence of burning rate on preignition temperature but also by a low dependence of burning rate on pressure, i.e., by both a low temperature coefficient and also a low pressure exponent n. 1

A further object is to provide a fuel that is essentially free from a form of eratic burning known as chuffing," and in which variation in the burning rate due to the erosion or pitting of the burning surface by the flow of gaseous products of combustion thereover is essentially eliminated.

Another object is the provision of a fuel of the character described, which may be manufactured in small sized granulations by solvent extrusion, the resulting grains being of such a character as to coalesce when dry pressed, thereby enabling the production of large size granulations as well as small size grains.

Another object is to provide a method of manufacturing a composite propellant in conventional solventextrusion type of equipment.

Other objects and advantages will be apparent as the invention is hereinafter more particularly described.

The foregoing objects may be accomplished in accordance with the present invention which is based in part upon the discovery that a modified double base type of propellant having significantly improved burning properties may be produced by either dry or solvent extrusion procedures, provided there is uniformly dispersed throughout the colloided double base dough, at any convenient stage prior to extrusion, a finely divided particulate filler having an explosive potential and comprising an oxidizing agent and a reducing agent, the filler being capable of reaction when the extruded and dried composition is burned to produce large quantities of gaseous reaction products.

The extruded and dried propellant produced by this procedure may be regarded as a double base matrix having a substantial proportion of chemically active particles uniformly distributed throughout the composition. The powder is therefore heterogeneous in the sense that minute areas of the composition that produce a strongly oxidizing gas, for example, are specially separate by finite but very small distances from other areas that produce a strongly reducing gas. However, the composition is homogeneous in the sense that the heterogeneous filler is uniformly dispersed in the homogeneous explosive matrix.

Generally speaking, the minimum filler to matrix ratio required in order to attain a substantial improvement in the temperature coefficient of burning is less than that required for a material improvement inthe pressure exponent. Thus, for example, if a series of powders is made from a given particulate filler and a given double base matrix but with various filler-tomatrix ratios, it will be found that the pressure exponent of the finished powders will be substantially improved only in the case of those powders containing a relatively large proportion of filler (e.g., 30 percent or more) while the temperature coefficient of the finished powders will be improved in the case of powders con taining a smaller proportion (e.g., as little as 6 to percent) of filler, as well as in the case ofthose containing enough filler materially to improve the pressure exponent.

Actually the proportion of filler required to bring about a given improvement in either (1) temperature coefficient of burning or (2) both temperature coefficient and pressure exponent will depend in large measure on the particular components used in making the powders. Thus, for example, if the filler consists entirely ofoxidizing agents (no particulate reducing agent being used) then as much as 50 percent of filler may be required in a relatively oxygen deficient matrix before the temperature coefficient of the ultimate composition is significantly improved, while as much as 70-80 percent of the same filler will be required before the pressure exponent is also materially improved. On the other hand, if the filler consists of a relatively oxygenbalanced mixture of particulate oxidizing and reducing agents, then in some cases as little as 8l0 percent of the filler in an equally balanced double base matrix may be sufficient to improve the temperature coefficient while as little as 25-30 percent of filler may materially improve both the pressure exponent as well as the temperature coefficient of the ultimate powder.

It will thus be evident that the filler-to-matrix ratio necessary to bring about a given improvement in the temperature coefficient alone, or of the pressure exponent as well as the temperature coefficient, cannot be selected arbitrarily in advance but must be determined by test for each individual type of filler when used in combination with each individual type of double base matrix. However, the precise proportions required to attain the effects mentioned may readily be determined by preparing a series of powders from the same components but with progressively increasing proportions of filler, and then determining the temperature coefficients and the burning law exponents of the various powders.

The foregoing principles may be illustrated by reference to Table l which shows the approximate effect of various amounts of a filler consisting of 86 percent KClO, and 14 percent carbon black on a given double base matrix. It will be evident from the data given that the change in burning rate with pre-ignition temperature decreases enormously even with a relatively small increase in the proportion of filler, but that the exponent decreases to a material degree only if the filler content reaches a relatively higher level.

The chemically reactive filler employed in accordance with the present invention consists of particulate material that is substantially insoluble in the volatile organic solvent to be employed in compounding the plastic dough prior to extrusion. Since this solvent conventionally consists of a mixture of 1) alcohol and ether, (2) alcohol and acetone or (3) alcohol, ether and acetone, the choice of filler may conveniently be limited to solid oxidizing and reducing agents that are substantially insoluble in these combinations of solvents.

For the reasons explained above, the preferred oxidizing agents for use in preparing the filler consist of inorganic oxidizing agents such as the metal perchlorates or nitrates, for example the potassium, sodium or barium nitrates or perchlorates and the like. Likewise the preferred reducing agents consist of alcoholand/or etherand/or acetone-insoluble particulate reducing agents such as carbon (e.g., carbon black), or the inorganic salts of organic acids containing a relatively large number of carbon atoms, for example, ammonium picrate. Many other oxidizing and reducing agents suitable for the present purpose will readily be apparent to those skilled in the art.

Because of the very large number of possible combinations and permutations of filler and double base matrices, it will be convenient hereinafter to illustrate the invention by particular reference only' to those powders containing l either perchlorates or nitrates as the oxidizing agent with or without carbon or ammonium picrate as the reducing agent, in conjunction with (2) double base matrices prepared from nitrocellulose'plasticized with nitroglycerine. It should be clearly understood, however, that the specific examples hereinafter described are merely illustrative of the principles involved and are not intended to delinate the breadth of the invention or to limit the scope of the appended claims.

In short, the following examples merely constitute representative specific applications of the broad principles discussed above.

EXAMPLE I v The propellant of this example is characterized by the ballistic advantages of a composite propellant (e.g., low n, low temperature coefficient of pressure change, Etc.) but may be prepared in ordinary solventextrusion equipment. Of the various ingredients that may be used in preparing this composition, the nitrocellulose, nitroglycerinc and centralite are the ordinary raw materials of the smokeless powder industry.

The carbon black should be a substantially pure carbon gas black having a specific gravity of 1.75 which may be obtained as a commercial product and used without further processing. The KClO is of Army Ordnance. grade for pyrotechnics, preferably blended with a 0.5 percent magnesium oxide and then ground in a micropulverizer. After grinding, the material is preferably blended with 0.5 percent magnesium stearate by screen, the stearate serving as an anti-caking agent and also as an-aid in extrusion.

The particle size distribution may be determined by means of a sub-sieve sizer and'measuring the retention on a 325 mesh screen. The preferred KClO, specifications for this particular powder call for an average particle diameter of 7.5 i 0.5 mu as measured by a subsieve sizer and a 325 mesh' screen retention of 6 percent.

The composition of the preferred powder is as follows:

Nitrocellulose (N.C.) (12.6% N) 21.0% Nitroglycerine (N.G.) 13.0 KClO, 55.4 Carbon black 9.0% Centralite No. 1 1.0 Magnesium oxide 0.3 Magnesium stearate 0 3 The solvent used is preferably 60 percent ether, 30 percent alcohol and 10 percent acetone; the weight of solvent used is percent of the weight of the dry ingredients.

1n the preparation of this composition, counterrotating sigma blade mixers are suitable. The preferred mixing procedure followed is to mix the alcohol-wet nitrocellulose, carbon black, KClO and the remainder ofthe alcohol for 10 minutes at room temperature; add

4 with one-half the ether; mix for five minutes; add the rest of the ether; and then mix at 15C. for an additional minutes.

The next step in the preparation of the powder may be a spaghetti process. The material as it is taken from the mixer, containing approximately 15 percent solvent, may be loaded into the press and extruded through a 50 to 80 mesh screen and a multiperforated die having holes 0.050 inch in diameter. During the spaghett process work is done on the composition, uncolloided nitrocellulose is removed and one or two percent of solvent is lost. The spaghetti process appears to aid in proper compounding, however, samples have been compounded successfully with this step omitted.

For the final extrusion the spaghetti is loaded into the material cylinder while the cylinder is being filled through the barrel of the die with C0 The die assembly, of conventional type, consists of screens, support plate, die holder, pin bridge, agate and pin. Extrusion is carried out at pressures and rates which seem to give optimum surface quality to the preparation. Extrusion pressures vary with die size and with type and amount of solvent. For example, the composition as prepared above extrudes at 3,000 to 6,000 p.s.i. on the material with an 0.414 inches diam. die and at 8,000 to 10,000 p.s.i. with an 0.134 inch diam. die.

With compositions containing magnesium stearate, the spaghetti may be extruded at a rapid rate, averaging approximately 10 feet per minute with the 0.414 inch die. Common surface flaws found in extrusion give little trouble with properly compounded dough. Without the use of magnesium stearate as an extrusion lubricant, considerable trouble is experienced with cracked and torn surface. Properly prepared grains of this composition have a mirror-smooth surface.

The powder is finished in a conventional manner for solvent-type, large web, double-base powder using the usual facilities and equipment. A typical drying schedule in a forcedair type dry house for a stick of 0.92 inch o.d. would be: 48 hrs. at 25C., 216 hrs, at 2555C. during which the temperature is raised 1 every 5 hours until 55C. is reached, and finally 48 hrs. at 60C.

EXAMPLE 11 EJ-B BBP Nitrocellulose (NC.)(13.1% N) 42.0% 54.6% Nitroglyce'rine (N.G.) 26.5 35.5 KClO, 25.8 7.8 Carbon black 4.2 1.2 Centralite 1.5 0.9

The KCIO, is ground to the same specifications as in Example I. A 60-40 acetone-alcohol solvent is used, the amount being 20 percent of the dry weight of the ingredients.

The dough is taken directly from the mixer to the tinishing press. No Spaghetti" step is necessary, the

EXAMPLE 111 The composition of this example is one containing only a crystalline oxidizing agent as filler in a plastic matrix. It is characterized by a fast linear rate of burning and low coefficients of pressure and temperature for the rate of burning. Its composition is as follows:

Nitrocellulose (N.C.)(12.6% N) 20.0% Butyl Stearate 9.0 Diphenylamine 1.0 KCIO. 70.0

32 percent of 67-33 ether-alcohol is used in thepreparation of this propellant. The other details of the preparation are similar to those described in Example 1.

EXAMPLE IV For certain applications, particularly those in which a fairly slow linear rate of burning is desired, compositions containing potassium nitrate and carbon as the filler in a double-base matrix are useful. The preparation of propellants of this type is similar in most respects to the preparation of those described above. A typical composition is as follows:

The KNO is prepared for incorporation by grinding in a micropulverizer, classifying in an air classifier and finally by an appropriate screening treatment. 44 percent of a 60-30-10 ether-alcohol-acetone solvent mixture has been used in compounding the composition. The pressing procedure (both spaghetti and finishing pressing) is similar to that described in Example 1. A typical drying schedule (for a 1.2 inches o.d. grain) is as follows: For the first 3 weeks of drying the powder is covered with canvas sacks. The powder is held for 168 hours at 25C.; for 360 hours at 25-55C. while the temperature is raised 1C. every 12 hours until 55C. is reached; and finally for a maximum of 192 hours at 55C.

The preparation and properties of several compositions containing alternative ingredients or different proportions of components, are given in Table [1.

EXAMPLE V Preparation and Properties of Solventless or Dry Extruded Composites The ballistic advantages of a large web make the production of large grains by solventless extrusion quite attractive. Solventless extruded composite grains have been successfully produced by a combination of solvent and solventless extrusion processes, as described below.

The 3/8 inch solid rods having the following composition are made up by the procedure described in any of 0 the foregoing examples:

Nitrocellulose (N.C.)(12.67z) 23.071 Nitrocellulose (N.C.)( 12.6% N) 26.0% Nitroglycerine (N.C.) 22.0 Nitroglycerine (N.C.) 22.0 KCIO. 43.1 n 43.0 I Carbon black 6.9 Carbon black 7.0 Centralite 5.0 Centralite 2.0 Candellilia Wax 0.2

Table 11 Miscellaneous Examples of of N V! 7! V1 '7! Other Type N.C. 1n N.C. Cent. N.G. KClO Solvent Ingredients Purpose Results PP 22.0 13.1 2.0 21.0 18.5 Nitroguanidine High specfic impulse High impulse 75-25 48.0 Low rate ace.-alc. Al flake 7.0 Poor n- OP 40.0 13.4 5.0 25.0 32.0 NaNO;, 30.0 lmproved temperature Fair 75-25 ace-ale. coefficient VP 28.0 13.4 1.0 27.0 NaNO 40.0 lmproved temperature Good 75-25 ace-ale. Dicyandiamide 24.0 and Press.

DlNA 7.0 Coefficient ZP 22.0 11.0 25.0 34.0 Fivonite 30.0 do. Fair 22.0 13.4 75-25 ace.-a1c. Diphenylamine 1.0 0.1 19.5 12.6 1 5 24.5 40.0 Am. picrate 17.5 do. Good 19.5 13.4 60-35-5 KNO; 17.5

eth.-alc.-ace. Beeswax 0.1 A] 30.0 12.6 1.0 19.0 20.0 40.0 Nitroguanidine 21.0 do. Good 60-30-10 eth.-a1c.-ace. GC 21.0 12.6 0.5 13.5 32.5 Guanidine Picratc 26.0 do. Good 60-30-5 KNO 390 eth.-a1c.-ace. E] 19.0 12.6 1.0 15.0 56.0 30.0 Carbon black 9.0 lmproved drying Good 60-30-10 properties eth.-a1c.-ace. FJ 18.0 13.1 2.4 29.6 14.9 36.0 Carbon black 51 lmproved ballistics Fair 55-30-15 with low filler eth.-alc.-nce. 1i] 21.0 1 .6 1.0 13.0 53.5 30.0 (ttrlion blltuk 11.5 lmproved ballistics Fnir -30-10 with low oxygen cllr-nle-ncc. lmlnncc in l'lllcr Twenty-five percent of the 60-30-10 ether-alcoholacetone mixture is used. The 3/8 inch solid rods are cut into short lengths and dried to less than 1 percent total volatile content. This stock is then poured into the barrel of a solventless extrusion press, after preheating to 60C. and extruded following the usual technique of solventless extrusion. Solventless extruded grains prepared with this technique have shown marked ballistic improvement over present solventless extruded propellants.

Advantages ofthe Invention The extruded composite propellants as a class have many outstanding advantages; including the following: 1. A low temperature coefficient of burning i.e., a low-rate of change of equilibrium pressure as a function of preignition temperature when the material is burned in a rocket motor at a constant ratio of burning area to ble to tailor a propellant charge for a given rocket motor.

6. In the case of the powders containing a high filler content, a low pressure exponent, n, which means that the equilibrium pressure of such powders is less sensitive to fluctuations in burning surface or other nsiitions...

It will be apparent to those skilled in the art that a large number of variations may be made in proportions. components and methods of preparation'of the improved propellant compositions of the present invention. All such changes and variations will be readily apparent to those skilled in the art. We therefore intend to be restricted only in accordance with the appended patent claims.

We claim:

1. A new article of manufacture,-a propellant comprising about 21.0 percent nitrocellulose, about 13.0 percent nitroglycerine, about 55.4 percent potassium perchlorate of an average particle diameter of 7.5 i 0.5 mu, about 9.0 percent carbon black, about 1.0 percent centralite No. l, 0.3 percent magnesium oxide and 0.3 percent magnesium stearate, the nitrocellulose and nitroglycerine being colloided and intimately mixed with the other ingredients to form a matrix in which the particles of potassium perchlorate and carbon black are distributed. 

1. A NEW ARTICLE OF MANUFACTURE, A PROPELLANT COMPRISING ABOUT 21.0 PERCENT NITROCELLULOSE, ABOUT 13.0 PERCENT NITROGLYCERINE, ABOUT 55.0 PERCENT POTASSIUM PERCHLORATE OF AN AVERAGE PARTICLE DIAMETER OF 7.5 $ 0.5 MU, ABOUT 9.0 PERCENT CARBON BLACK, ABOUT 1.0 PERCENT CENTRLITE NO. 1,0.3 PERCENT MAGNESIUM OXIDE AND 0.3 PERCENT MAGNESIUM STEARATE, THE NITROCELLULOSE AND NITROGLYCERINE BEING COLLOIDED AND INTIMATELY MIXED WITH THE OTHER INGREDIENTS TO FORM A MATRIX IN WHICH THE PARTICLES OF POTASSIUM PERCHLORATE AND CARBON BLACK ARE DISTRIBUTED. 